With the advent of mechanized society within the United States and around the world, the need for lubrication and hydraulic fluids has been ever increasing. A finite supply of petroleum based products plus concerns over environmental effects from spills/disposal of petroleum based lubricants has fueled interest in the use of vegetable oils as viable substitutes.
Efforts in use of vegetable oils as the base oil have focused upon less stringent uses such as hydraulic fluids, transmission fluids, and greases and not on the more severe automotive-type (engine) lubricants. The vast majority of these endeavors have utilized vegetable oils high in natural oleic acid levels such as safflower oil and rapeseed oil. The reason for this focused research upon these high oleic acid level vegetable oils is the tendency of natural vegetable oils to destabilize in use absent the presence of a high level of oleic acid. Soybean oils have a low level of oleic acid and been uniformly rejected in practical application because of the tendency of soybean oil to solidify while in use within the environment of the machinery.
The primary purpose of hydraulic fluids is to maintain lubrication and fluid characteristics while in use within the system so as to maintain appropriate pressure to operate hydraulic actuators (cylinders/motors) assemblies in machinery on demand. In order for appropriate pressures to be maintained within a hydraulic system, the fluid is constantly being run through a pump. The constant pumping action creates a substantial build up of heat in use, which the vegetable-based hydraulic fluid must withstand. Additionally, the operation of the hydraulic actuators and the process of constantly pumping the vegetable-based hydraulic fluid subjects the fluid to constant mechanical stresses. Vegetable oil based hydraulic fluids have found commercial success in certain industrial applications. These applications present a much less demanding environment in which the vegetable oil based hydraulic fluid must function. Specifically, the industrial applications present an environment where the hydraulic fluid is cooled so as to control and maintain a relatively stable temperature. Variations in temperature, in particular high temperature environments, are known to impact the ability of a vegetable oil based fluid to remain in the liquid state. As a result, this limited application within the industrial setting has been an area in which vegetable oil based hydraulic fluids have been found to function with relative success, and represents the vast majority of commercial settings in which vegetable oil based hydraulic fluids are found in use at the present time.
Use of vegetable oil based hydraulic fluids in the out-of-doors environment presents a much harsher challenge. To date, the success of such fluids has been very limited. Rapeseed oil based hydraulic fluids recently have been commercially offered, but questions remain as to the functionality of these hydraulic fluids in the out-of-doors environment, particularly within mobile equipment.
A use presenting the harshest conditions for hydraulic fluids is within agricultural tractors. Tractors are required to function in all temperature conditions, performing a variety of mechanical operations. In use, tractor hydraulic fluid must successfully operate not only the actuators of the hydraulic system, but must also work well within the brake assembly. The key characteristics required for mobile hydraulic fluid use are:
1. High oxidation stability PA0 2. Viscosity Characteristics PA0 3. Extreme Pressure Performance PA0 4. Corrosion Inhibition Properties PA0 5. Seal and Polymer Compatibility PA0 6. Foam Suppressed PA0 7. Controlled Friction
for long life and protection PA1 small sump capacity PA1 high temperatures (170.degree. C.) PA1 air entrainment PA1 reduced flow rates PA1 increased deposits PA1 low pour point for flow temperature service, particularly during PA1 cold starts PA1 high Viscosity Index for best viscosity under various operating PA1 temperatures PA1 increased wear protection under heavy and shock loads PA1 very high pressures (6,000 to 10,000 psi) PA1 material limitations PA1 contaminants in the fluid PA1 water PA1 oxidation by-products PA1 old and new hoses PA1 seal materials PA1 air entrainment PA1 Operating System Components PA1 valves PA1 clutches PA1 brakes PA1 cylinders PA1 motors PA1 pumps
Stationary (indoor) hydraulic systems may not require all of the above properties, although most still apply. The characteristics required in order to operate the braking system involve the normal demands placed upon hydraulic fluid, but also include that the fluid withstand the mechanical sheer forces of dampening the braking action of the assembly. These mechanical sheer forces operate to degrade the hydraulic fluid.
A final demand placed upon tractor hydraulic fluid is the requirement that it function as a transmission fluid. Accordingly, it must withstand greater amounts of heat generated within the operational environment and must have frictional qualities that allow the gears of the transmission to interact. In many instances, these requirements of tractor hydraulic fluid are competing, placing additional demands upon the hydraulic fluid.
Certain of the applications of vegetable oil based hydraulic fluids have resulted in the issuance of patents. One such patent is U.S. Pat. No. 4,783,274. The primary focus of the U.S. Pat. No. 4,783,274 is the use of rapeseed oil as the base component of hydraulic fluid. A review of the data contained within the specification for the patent reveals that none of the bench tests of the subject hydraulic fluid appeared to use any vegetable oil component other than rapeseed oil. Although other oils were included, i.e. olive, peanut, and corn, no mention of soybean was made. Further, the U.S. Pat. No. 4,783,274 covers a hydraulic fluid utilizing vegetable oils comprising 85%-99% of the fluid by weight. As a result, the teachings of the U.S. Pat. No. 4,783,274 are limited to the effectiveness of rapeseed oil based hydraulic fluids within the laboratory environment.
Another prior art patent is U.S. Pat. No. 5,454,965 which is based on utilization of telomerized oil made of about 20% to about 70% of a conjugated triglyceride oil. While the broad description of the triglycerides in this patent may encompass the soybean oil, the U.S. Pat. No. 5,454,965 is mainly concerned with the telomerized triglyceride as a performance enhancing additive for use in industrial lubricants applications. It does not refer to a partial hydrogenation process, nor the specific application for which the present invention is designed.
Another prior art patent, U.S. Pat. No. 5,567,345, is also based on the telomerized oil made up of triglycerides. Again the use of term triglyceride is all encompassing and includes oils such as soybean oil. The telomerized oil described in the U.S. Pat. No. 5,567,345, however, is a blown oil designed to be used as a thickener additive for high viscosity oils in the ranges of 5,000 to 12,000 SUS @ 40.degree. C.
U.S. Pat. No. 5,451,334 is for hydraulic fluid based on rapeseed and soybean oil. The base oil described in this patent is purified rapeseed or soybean oil. While these oils may perform in low demanding industrial stationary equipment, they have not shown to perform in demanding mobile equipment. Hence, a process of hydrogenation is necessary to obtain optimum stability needed for such applications.
Still another prior art patent, U.S. Pat. No. 5,380,469, relates to high viscosity functional fluids prepared by reacting polyglycerol with a triglyceride oil or fat. The patent refers to triglycerides and vegetable oil in an all-encompassing fashion. This patent is, however, specifically concerned with reacting a polyglycerol with a triglyceride oil or fat. Specifically, canola oil is identified as the preferred triglyceride. Furthermore, this patent is concerned with controlled polymerization as a means of increasing the viscosity of the fluid and changing its solubility, and also deals with high viscosity functional lubricants having viscosity ranges of 2,000-2,500 cSt @ 25.degree. C.
In view of the state of the prior art as summarized above, there is a need for an improved non-petroleum based, environmentally safe oil that can be commercially used in the hydraulic systems of mobile outdoor equipment that is operated under widely varying conditions.